Croissance en diamètre et caractérisation de la limite entre bois juvénile et bois adulte chez l’okoumé des plantations au Gabon

Abstract

Stokes. Radial growth and characterization of juvenile and adult wood in plantation grown okoumé (Aucoumea klaineana Pierre) from Gabon. Annals of Forest Science, Springer Verlag/EDP Sciences, 2007, 64 (8), pp.815-824. <hal-00884137>Ann. For. Sci. 64 (2007) [815][816][817][818][819][820][821][822][823][824] Abstract -The fast-growing hardwood, okoumé (Aucoumea klaineana Pierre), is a major forest species in Gabon and is used principally for making plywood, but research into the growth and quality of this wood is scanty. Trees from natural forests are favoured for production, yet little information exists on wood characteristics from plantation trees. Therefore, we carried out a dendrochronological study along with measurements of wood longitudinal modulus of elasticity (E L ), density (D w ), dimensional stability parameters (longitudinal, radial and tangential shrinkage and fibre saturation point) and fibre cell morphology to determine if these properties were related to age in trees from two plantations. We then used segmented regression analysis to define the limit (breakpoint) between juvenile (JW) and adult wood (AW). Using monthly precipitation data, we were able to determine that one growth ring is formed per year, composed of a large light coloured ring formed during the long rainy season and a thick, dark band formed during the major dry season. However, thinner bands, analogous to false rings, may also form during the short dry and short rainy seasons. Ring width decreases from the pith to the bark, and the breakpoint between JW and AW was at 19 years old when trees from both plantations were pooled together. No differences in D w or radial and tangential shrinkage occurred with cambial age. E L increased significantly up to the cambial age of 12-14 years, after which the increase with age was only slight and no breakpoint between JW and AW was found. With regard to mean longitudinal shrinkage, AW was found to form after the age of 13 years but fibre cell length was significantly longer after the age of 14.5 and 20 years, depending on the plantation of origin. Therefore, the boundary between JW and AW in plantation grown okoumé occurs between the ages of 13 and 20 years, depending on the characteristic examined. dendrochronology / modulus of elasticity / wood density / shrinkage / fibre saturation point Résumé -Croissance en diamètre et caractérisation de la limite entre bois juvénile et bois adulte chez l'okoumé des plantations au Gabon. L'okoumé (Aucoumea klaineana Pierre) est une essence à croissance rapide que l'on rencontre majoritairement au Gabon. Son bois est principalement utilisé dans la fabrication de panneaux de contreplaqué. Cependant les recherches sur la croissance et la qualité de son bois ne sont pas suffisamment avancées. L'utilisation des arbres issus des forêts naturelles est favorisée pour la production par rapport à ceux issus des plantations dont les caractéristiques sont peu connues. De ce fait, nous avons entrepris d'étudier la dendrochronologie des okoumés dans les deux pla...

Which factors most influence heartwood distribution and radial growth in plantation teak?

“…The program SegReg (Oosterbaan, 2005) was used to carry out segmented linear regression analysis on mean ring width with cambial age, to estimate the age limit between the formation of JW and AW (Alteyrac et al, 2006;Bhat et al, 2001;Medzegue et al, 2007) in each size class of trees. Although several wood anatomical and physical properties are necessary to determine correctly the breakpoint between JW and AW, we can nevertheless obtain useful information concerning the influence of status on one predictor of AW and AW formation.…”

“…juvenility and ageing, because teak has a longer period of juvenile wood (JW) formation in certain locations where trees grow fast (Bhat et al, 2001). JW is formed from a juvenile cambium during the early years of physiological activity (Bhat et al, 2001;Medzegue et al, 2007;Zobel and van Buijtenen, 1989). Adult wood (AW) is then produced and usually has thinner annual growth rings, a higher longitudinal modulus of elasticity (E L ), higher density and greater dimensional stability due to changes in xylem structure.…”

Relationship between ecological indicators and teak wood characteristics in Tchorogo plantation (Togo)

“…Then, it could be considered that in Togolese teak plantation, the critical age of demarcation between juvenile and mature wood was somewhere between 20-25 years. Juvenile wood is formed from a juvenile cambium during the early years of physiological activity (Zobel and van Buijtenen, 1989;Bhat et al, 2001;Medzegue et al, 2007). Mature wood is then produced and usually has thinner annual growth rings, a higher longitudinal modulus of elasticity (E L ), higher density and greater dimensional stability due to changes in xylem structure.…”

Impact of cyclic compressive loading and moisture content on the mechanical behavior of Aucoumea Klaineana Pierre

“…In central Africa and particularly in the equatorial region, the forest plays a key role in regulating our environment by sequestering greenhouse gases (Odounga et al 2016). In the year 2000, Gabon produced over 4 million m 3 of timber (Medzegue et al 2007), of which 72% was Aucoumea Klaineana Pierre (AKP). This species is mainly used for plywood construction, in veneer, and finished or semi-finished products such as pulp and paper (Manfoumbi Boussoungou et al 2010, 2012.…”